Amplitude scanning of an antenna array on receiving



March 23, 1965 c. J. SLETTEN 3,175,156

AMPLITUDE SCANNING OF AN ANTENNA ARRAY 0N RECEIVING Original Filed Sept.5, 195a 4/? i4 4/ r ?4/ I I g W .1

INVENTOR 64/90 45 07:52 577677 United States Patent 3,175,156 AMPLITUDESCANNING OF AN ANTENNA ARRAY 0N RECEIVING Carlyle J. Sletten, Acton,Mass, assignor to the United States of America as represented by theSecretary of the Air Force Original application Sept. 3, 1958, ser. No.758,869, now Patent No. 3,085,204, dated Apr. 9, 1963. Divided and thisapplication Aug. 2, 1962, Ser. No. 214,436

1 Claim. (Cl. 325-180) (Granted under Title 35, US. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the United States Government for governmental purposes withoutpayment to me of any royalty thereon. I V

The invention relates generally to scanning antenna systems, and moreparticularly to a novel method and means for scanning an antenna beam onreceiving to generate many beams (multilobes) at many ports orterminals.

This application is a division of applicants co-pending application,Serial No. 758,869, filed September 3, 1958, now US. Patent No.3,085,204, entitled Amplitude Scanning.

Prior devices have utilized cumbersome mechanical means to produce arotation of the entire physical structure of an antenna in order to scanan antenna beam. Devices of this nature, in addition to being bulky, areexpensive and limited in the rapidity of the scanning op eration.

Electronic scanning antenna systems have been proposed wherein avariation of either the frequency or the phase of the energy along anarray is utilized to produce a beam movement; however, either a changein antenna dimensions or complicated, expensive devices are necessaryfor an accurate control of a beam of radiated energy.

The method and means forming this invention for electronic scanning maybe eifected by various means which easily and accurately change only theamplitude to elements of an array. This can be accomplished bycontrolling a voltage applied to grids of amplifiers which feed separateradiating elements in an array or by utilizing low powered transmittingsources on each radiated element and amplitude modulating these sources.Amplitude scanning also may utilize simple mechanical movement ofantenna elements for varying the coupling and thereby the amplitude tothe various elements.

Accordingly, it is an object of this invention to produce novel methodsand means for scanning a signal r receiving array by utilizing avariable gain radio frequency amplifier at each element of the array andcombining the output of these amplifiers to produce a steerabledirective receiving system or multiple beams from many receivers.

Other advantages, features and objects of the invention will become moreapparent from the following description taken in connection with theaccompanying drawing which is a partially schematic representation of anapplication of the amplitude scanning technique to an antenna array usedfor receiving a signal to produce multiple beams.

The mathematical approach to amplitude scanning is based on my copendingapplication No. 615,208, filed November 10, 1956, now US. Patent No.3,100,300, en titled Antenna Array Synthesis Method and Apparatus,wherein it is shown that quarter wave spaced radiators with alternateelements in phase quadrature may be used to synthesize any antennapattern. An extension of the principles taught in that application wouldallow for the creation of a sharp antenna pattern wherein the patternPatented Mar. 23, 1965 may be made to assume various angular positionsby varying the amplitude of the feeding coefficients in accordance withthe following analysis and theory.

In accordance with thetheory presented in my afore- 5 mentionedcopending application, the shape of a beam to be generated may beidealized and generated at a given angle, d with the normal to an arrayand determine the coeflicients C and B,,.

In accordance with the technique of the above theory,

a system is developed that approaches a uniformly illuminated array,wherein m 2;, sin (meow.- sin -H h v- Sin l where m is equal to 11-1.The displacement of the main beam from the perpendicular to the array isgiven by :1 (note that =sin a and =sin a). The feeding coefi'icients forthe array are given by the cos mryb and sin (mi /2)1ryb terms. Thedesired fixing phasing on the array can be obtained by comparing thefeeding coelficients of f (11/, p with the resolution of the radiatedpattern in terms of phase on a transmission line as given in theaforementioned copending application. The spacing between adjacentelements is M4.

Mechanical movement of antenna elements to achieve a variation incoupling, which in turn produces a variation in amplitude to the variouselements, and the utilization of angular positioning of an element on atwowire line to achieve a predetermined coupling, is taught in mycopending application, S. No. 613,011, filed October 1, 1956, now US.Patent No. 2,963,730, entitled Method and Means for Antenna Coupling. Anextension of this theory involves the rotation of these elements to varythe coupling and therefore the amplitude of the signal to each dipole tocause the scanning of an antenna beam.

The drawing illustrates the scanning of an array, on receiving, usingamplitude scanning techniques. Signals are received on the M4 spacedantenna elements. The line lengths are alternately changed at M4 valuesto create a 90 phase shift between the elements. These received signalsare then fed to preamplifiers 40 to raise the signal above the noiselevel while at the same time maintaining the phase of the signal at theamplifier input. The power is then divided, in this example, to twopairs of three variable gain amplifiers 41 or attenuators, one set ofwhich has the signal inverted 180 in a phase inverter 42. The cfirst,second and third of each pair g .to separate addition buses 43, 44 and45, respectively, and a summation of the signals from each element arecombined on the buses to give three beams. The buss or sum lines, 43,44, and 45, are assumed to sum signals without phase shift. This ispractical, using superheterodyning techniques common to receivers. Notethat the number of beams formed this Way need not correspond to thenumber of radiating elements in the receiving array. The gain ofamplifiers plus attenuator will be adjusted for each beam according toformula (column 2). A comparison of these beams may be used, forexample, to determine the location of a communication or radar signalsource. An application of amplitude scan on receiving, accomplished byusing a variable-gain radio frequency amplifier at each element of thearray and combining the output of these amplifiers, can be used toproduce a steerable directive receiving system or multiple beams frommany receivers.

Thus, it can be seen that amplitude scanning can be utilized for anyantenna array having equispaced elements in phase quadrature. Differentspacings between the elements would vary the pattern throughout thescan. Slight variations in phase as the amplitude is varied may betolerated; however, an appreciable variation would cause a deteriorationof the pattern as the beam is scanned.

Although the invention has been described with reference to particularembodiments, it will be understood to those skilled in the art that theinvention is capable of a variety of alternative embodiments within thespirit and scope of the appended claim.

I claim:

A means for amplitude scanning a received signal comprising an array ofantenna elements having a phase shift between adjacent elements, meansfor dividing the received signal of each of said elements between atleast two channels, means for phase inverting one of said dividedsignals 180, variable gain amplifier means adapted to receive dividedpower from the signals of each of said channels and means for summingthe resultant signals on each power level.

References Cited by the Examiner UNITED STATES PATENTS 3,056,961 10/ 62Mitchell 333- 3,085,204 4/63 Sletten 343-854 3,087,158 4/63 Fisch333-l00 ELI LIEBERMAN, Acting Primary Examiner.

HERMANN KARL SAALBACH, Examiner.

